I don't want to compress the lead or damage the polymer coating. Do the math. If your calipers show the diameter of a 9mm boolit is 0.356" (maybe 0.355) and that the thickness of the end of the case mouth where you will be taper crimping is 0.011" or maybe 0.012", then add it up. Even at the smallest values:
0.355 + 0.011 + 0.011 = 0.377"
If I use the larger values:
0.356 + 0.012 + 0.012 = 0.380"
I target 0.379", don't see any point in going smaller and overcrimping can cause other issues like tumbling, leading, etc. Not saying these things will happen with a few thousandths more taper crimp, but I don't see an upside either.
Are you now, or have you ever been a member of the Doodie Project?
Pretty sure I've got the crimp die set up right--just enough to remove any last bit of flare, not enough to really crimp anything.
I'll pull some rounds out tonight and measure the crimp, as well as clean out my case gauge. If I find a few that won't pass the case gauge I'll try a touch tighter on the crimp and see what happens.
Jeff Martin
What % of cases are failing CG? If it is acceptably small then just segregate failures and shoot in a form of practice where you can tolerate *possible* faiure to go into battery. The ones that pass go in to the match or practice bins when I will be shooting longer strings that I don't want interrupted with failures. Some guns (chambers, recoil springs, etc.) are more tolerant than others.
At <= 5% this is an easy decision for me. I'd like it lower but know my mixed brass has a lot of issues.
At >10% I start looking for incremental process improvements. I have seen cases where more cartridges failed than passed.
Are you now, or have you ever been a member of the Doodie Project?
Jeff Martin
I run range pick up brass in my Glocks. If I chamber gauge them I get 5 or 10 out of 100 that don't pass. Most will just not quite go down flush in the chamber gauge. I put them in the practice box and they usually run just fine. I think a lot of times the head is so beat up from being shot a bunch of times that they are swollen. Try putting them in the CG upside down and see how far they go.
Like others, I'll bet your crimp is the culprit.
I have seen this on one or two rounds per 100 commonly with 9mm range pickup brass. Since 9mm headspaces off the case mouth, my theory is that it is simply a matter of a few over length brass in the bunch. I segregate them and they typically work just fine in my glocks.
I find you can usually force the case further into the case gauge where it may or may not be flush and where it will stick and not fall freely out.
The idea of stretched 9mm brass is possible but I don't think it is the most common reason for case gauge failure.
Causes are numerous and include:
Bulges at the base of soft cases which have been squashed down vs. compressed in during resizing
Case bulges from not quite straight bullet insertion, or deeply seated bullets and a tapered case design
Bulges from less than fully supported chambers - might be mitigated by using a full length resizing die
Damaged case heads from guns that are rough on brass
Mysteries...
Are you now, or have you ever been a member of the Doodie Project?
Had a few rounds today that failed to go into battery when I was shooting today... they all failed the case gauge as well (obviously). They measured over 0.381" at the crimp (one was up around 0.386", I remember one round making it out without getting to the crimp station..found it!). I ran them through the crimp station again, and they came out at .380 or .381, and all passed the case gauge at that point. The OAL on all three was between 1.135 and 1.140". I'm going to dial the crimp down a touch more, try to get it to around 0.379, and see if I can get them a touch closer to 1.135".
Jeff Martin